This is a visually fascinating BBC documentary about the theory of evolution by Darwin. After watching the video, you can also have an interactive experience here: interactive Tree of Life. Darwin's theory may not be perfect, but it's the best we have so far. It is a pity some people (believers and non-believers) are presenting this theory as something opposed to the creation of life by God. Both ideas are perfectly compatible, nobody said that God can only act through miracles. A miracle is the exception, not the rule, and religious books are teachings of faith and life, not manuals of science.

A hundred and fifty years after the publication of Darwin's revolutionary book, modern genetics has confirmed its fundamental truth. All life is related. And it enables us to construct with confidence the complex tree that represents the history of life. It began in the sea, some three thousand million years ago. Complex chemical molecules began to clump together to form microscopic blobs: cells.

These were the seeds from which the tree of life developed.

They were able to split, replicating themselves - as bacteria do. And as time passed they diversified into different groups. Some remained attached to one another so that they formed chains. We know them today as algae. Others formed hollow balls which collapsed upon themselves, creating a body with an internal cavity. They were the first multi-celled organisms. Sponges are their direct descendants.

As more variations appeared the tree of life grew and became more diverse. Some organisms became more mobile and developed a mouth that opened into a gut. Others had bodies stiffened by an internal rod. They, understandably, developed sense organs around their front end.

A related group had bodies that were divided into segments with little projections on either side that helped them to move around on the sea floor. Some of these segmented creatures developed hard protective skins which gave their bodies some rigidity. So now, the seas were filled with a great variety of animals.

And then around 450 million years ago some of these armoured creatures crawled up out of the water and ventured on to the land.

And here the tree of life branched in to a multitude of different species that exploited this new environment in all kinds of ways. One group of them developed elongated flaps on their backs, which over many generations eventually developed into wings. The insects had arrived. Life moved into the air and diversified into myriad forms.

Meanwhile, back in the seas, those creatures with a stiffening rod in their bodies had strengthened it by encasing it in bone. A skull developed with a hinged jaw that could grab and hold on to prey. They grew bigger and developed fins equipped with muscles that enabled them to swim with speed and power. So fish now dominated the waters of the world.

One group of them developed the ability to gulp air from the water surface. Their fleshy fins became weight-supporting legs and 375 million years ago, a few of these backboned creatures followed the insects on to the land. They were amphibians with wet skins and they had to return to water to lay their eggs.

But some of their descendants evolved dry scaly skins and broke their link with water by laying eggs with watertight shells. These creatures, the reptiles, were the ancestors of today's tortoises, snakes, lizards and crocodiles. And of course, they included the group that, back then, came to dominate the land: the dinosaurs.

But 65 million years ago, a great disaster overtook the Earth. Whatever its cause, a great proportion of animals were exterminated. All the dinosaurs disappeared - except for one branch, whose scales had become modified into feathers. They were the birds.

While they spread through the skies, a small, seemingly insignificant group of survivors began to increase in numbers on the ground beneath. These creatures differed from their competitors in that their bodies were warm and insulated with coats of fur. They were the first mammals. With much of the land left vacant after the great catastrophe they now had their chance. Their warm insulated bodies enabled them to be active at all times - at night as well as during the day - and in all places: from the Arctic to the tropics, in water as well as on land, on grassy plains and up in the trees.

Today, we and the rest of the mammals share the world with the descendants of those other great animal groups that have evolved on this planet: with birds, with reptiles, with insects and with fish. And even with the simplest of all living organisms that first appeared over 3000 million years ago: with bacteria.

GENETICS= The name of the science investigating the genes (molecules of ADN that have the instructions to build our body).

IT ENABLES US= It allows us.

TREE= The word TREE is not used here to refer to the big plant. We can also use the word tree for the metaphorical idea of something that is growing and separating in different branches, like the "genealogical tree" (representing the generations of descendants in a family) or "the tree of life" (representing the evolution of creatures over millions of years).

CLUMP TOGETHER= Stick together, make groups.

BLOBS= A soft, amorphous mass.

SPLIT= Separate.

BACTERIA= Plural form of the word "bacterium" (one bacterium, two bacteria). A microscopic unicellular animal.

ALGAE= The plural form of "alga" (One alga /ælgə/ two algae /ælgi:/ , or more usually /ældʒi:/ ). Plants living in the sea. They may be unicellular and float in the water, or multicellular and be up to several meters long. We commonly use the term "alga" just for the microscopic and tiny organisms, and for larger plants we prefer the term "seaweed".

HOLLOW= Something hollow is empty inside.

UPON= On (old fashioned).

MULTI-CELLED= With many cells. The opposite is UNICELLULAR, with just one cell.

SPONGE= Pronounced /spʌndʒ/ . A sea animal, soft and fluffy, similar to the sponge we use in the bath (see picture here).

DIVERSE= Pronounced /daɪvɜ:s/ . Differing one from another.

STIFFENED= Made rigid. The opposite is "softened", made soft.

ROD= A thin straight piece of hard material.

VARIETY= /vəraɪətɪ/ .

ARMOURED= Having an armour (see picture). But also use for shells or a hard outside cover in general.

CRAWL= This is the way small animals move, like insects.

VENTURE= If you venture in a place, you take the risk of getting there, even if it is unknown and risky, like an adventure.

THE TREE OF LIFE BRANCHED= The tree grew a new branch, a new kind of animal appeared.

SPECIES= Pronounced /spi:ʃi:z/ . Different kinds of animals. Animals of the same specie ( /spi:ʃi:/ ) can reproduce together and have descendants.

ELONGATED= Extended, long.

FLAPS= A flap is a flat thin piece of material attached on one side.

MYRIAD= A very very large indefinite number.

BACK IN THE SEAS= If we are talking about place A, and then we talk about place B, and later we want to talk again about place A, we use the expression "back in A" to mean that we go back to the previous place or topic. So when he says "back in the seas", he doesn't mean that the animals go back to the sea, he only says that he is going to talk again about what was happening in the sea at that time.

BY ENCASING IT IN BONE= If you encase something in a material, you enclose it in that material, as when you put something inside a case. So the rod is now covered with bone.

SKULL= The bones in our head protecting our brains.

A HINGED JAW= A door has hinges (see picture) to connect it to the wall, so it is well connected but, at the same time, it can open and close. An animal has jaws connected to the skull, but they can open and close, so they are hinged, like a door (see picture of a jaw)

PREY= An animal hunted for food. For example, a lion is a predator and a gazelle is its prey.

GULP= To swallow rapidly in large amounts.

SURFACE= Pronounced /sɜ:fɪs/ . The outer superficial part of something. The surface of the water is the upper area where the water is in contact with the air.

FLESHY= Made of flesh. The human body is mainly made up of flesh and bones.